Yesterday we had our first major hydro outage. A short but severe storm blew through our neighbourhood with recorded gust of up to 125 km/h winds. This just makes category 1 hurricane speed. This occurred in the early afternoon before 3pm and then the power immediately cut out after that. A photo taken from one of our neighbours clearly showed down power lines.
Downed hydro poles near our house (compliments from our neighbour)
We had a few flickers and then our backup solar and batteries kicked in. I took the entire system off grid to avoid any on grid glitches and also as an extra safety measure for the working crews on the power lines. At first the solar was generating enough power to both cover the house load and charge the batteries. Once the batteries were fully charged, I took the panels offline until night time, because the extra power will have no place to go.
When night came on our block, we were the only house that kind of shined. Although others were suffering from a lack of power and wholly I empathized, It was a good silver lining to see our house with electricity.
House lights clearly evident during power outage in the evening
We are now in the morning after. The grid electricity was restored about 30 minutes after midnight. The outages lasted near 10 hours, quite a long one.
We were extremely fortunate to have our solar project completed on May 4th, and in less than 3 weeks we experienced this outage.
I am now going to flip the switch and go back onto the grid, so we can recharge our batteries in case anything else happens to the grid during the restoration process.
In a series of posts, I have documented my experiences and adventures on installing solar panels and backup batteries. One of the incentives that prompted us to start the project is the new Canada Greener Home Grant, which offers a maximum of $5,000 grant towards certain home projects that are classified as “green”. I also mentioned EnerTest as a great company that chaperoned us the entire process of the Canada Greener Homes Grant.
EnerTest was extremely prompt in organizing and conducting the energy audits, which are required for the grant eligibility. I wanted to thank Nick Crosby from EnerTest who played a very supportive role in guiding our family through this, and sometimes very confusing process.
Knock on wood, but I think today we crossed the last hurdle.
Confirmation from Canada Greener Homes Grant Web Site
If you are embarking on the same grant, take note that you must perform the first energy audit prior to you getting the work done. This is very important.
You will have to perform a second audit once all the work is completed. Make sure you keep all of your receipts and working documents relating to the work.
I would highly recommend Nick Crosby for the job if you are starting a similar journey that I did. Click on his name to email him.
It certainly feels good that the grant is coming our way in 30 days!
We now have been running our net smart meter for more than a day now. I mentioned that we got our new net meter on this previous post.
Of course I am now curious how to read the meter so that I can decipher how much electricity we sent back to the grid. Here is a short video of what the meter is showing:
Meter Display Sequence
Initially the displayed information is quite cryptic, but looking at the meter’s label, I found this group of small prints.
These labels essentially tells us what is going on. The LED display cycles through 5 modes in total. The initial display is a segment test, which means all segments of the LED are displayed. This is a simple test to ensure that the LED display itself is functioning correctly. Next, it shows LST003, indicating that the next number it shows will be the amount of kWh of electricity that we ended up consuming or using. This is followed by LST004, another label indicating that the following number is the amount of kWh of electricity that is sent back to the grid.
Now with this new found knowledge, the above video shows that we used 13 kWh and exported 103 kWh since the meter was installed in the afternoon of May 4th.
In about 1.5 days, and bright sunny day yesterday, we generated and provided to our community electricity grid with a net of 90 kWh of energy.
Excerpt from the CBC article from Oct. 8th, 2021
There are 4 people in our house right now, and according to a recent CBC article our average carbon footprint is about 14.2 tonnes of CO2 per person. Doing a little more research, I found this white paper titled, “A Clearer View on Ontarios Emissions June 2019“. On page 8 of this paper, we see an annual average emissions factor (AEF) of 31 grams of CO2 per kWh. One tonne is 1,000,000 (a million) grams. This means to offset one individual, we need to offset 14,200,000 grams of CO2, and using the AEF this is equivalent to approximately 458,065 kWh!
To put this big number in perspective, I think our last month’s electricity bill only shows us using around 1,200 kWh of electricity.
It is clear that we will not be able to offset one of us, never mind all four of us by just using solar ourselves (at least not in Ontario). The idea of carbon neutrality is still a long ways off, and the above numbers show that we cannot do it alone. It will require every industry to do its part.
Update 2022-05-26 2:45pm: Took another reading outside. Used 313 kWh, Exported 1018 kWh, a net of 705 kWh. This with about 23 days of operation since May 04th.
Today is a good day. Alectra finally installed the net meter. From my previous post, I noted that without a net meter, any excess energy being sent back to the grid will be interpreted as usage. With the addition of the net meter, we can finally export our excess electricity from our solar panels without being charged for the generation. Instead, we can start earning and storing credits for the excess energy that we will supply to the grid.
Prior to the presence of the net meter, we gained plenty of experiences on going off grid. Effectively even on a cloudy day, we were able to generate enough energy for the house and charge our batteries to get us through the night. Below is a depiction of our energy utilization from Alectra.
Started to go off grid on April 23rd
The process of getting this net meter installed was not an easy feat! It took 22 days from the time of ESA inspection (April 12th) to Alectra installing the net meter. In summary, we played with the solar system to see what it can do for 11 days (April 12th to 22nd), while paying for the excess generation, and went off grid for the remaining 12 days (April 23rd to May 4th).
The small usages from the 23rd to the 30th that you see above were primarily charging our Toyota Prius Prime from the garage. That circuit is still grid tied and is independent of our Solar system. I cannot get an updated chart that contains data all the way up to today. Perhaps Alectra is doing something in the background in preparation for them to switch to net metering. In summary, we were pretty much off grid from April the 23rd to around 2pm today (May 4th). There was one exception, when we charged our backup batteries during off-peak hours from the grid on the evening of the 26th. We didn’t have to, but I was bit anxious with the battery at 50% whether it will last through the night and to the next evening, so this was more of an insurance. As we get more experience, we now have the confidence that even during cloudy / rainy days in the month of April, we should have no problem charging the batteries from solar that will last to the next night time operation.
Our old unidirectional meter
Our new bidirectional net meter
Once again, I have to thank New Dawn Energy Solutions for their correspondence and baby sitting the net meter installation process, as well as closing out the building permit from Richmond Hill. I am certain there was plenty of red tape that must be cut by them to get to where I am today, so kudos to them!
Today was also the day when we completed our second audit with Enertest. Once again Nick Crosby, A Certified Energy Advisor did a professional job. This audit is mandatory for the participation of the Canada Greener Homes Grant program.
If you are thinking of installing solar, New Dawn and Enertest are partners and experts in your endeavours.
In my previous post, all major installations were completed. Since that time, the ESA inspection was completed and we validated our batteries so that we have confidence that they will last for more than a day in the worst case scenario (no sun). However at the time of this writing, we are still waiting for Alectra Utilities to switch out our old meter to a new one that is net-meter capable. Until this meter replacement occurs, every watt-hour (Wh) of energy we produce and send back to the grid, Alectra will charge us for it as if we are using that energy instead of producing it. Here is a summary of the timeline from panel installation:
Solar panels installation completed on April 8th;
ESA Inspection on April 12th;
New LiFePO4 batteries installed on April 18th;
From April 18th onwards, we tested the system through a series of scenarios;
Our Utilization Chart from Alectra Utilities (click to enlarge)
So prior to the ESA inspection on April 12th, we continue our on-peak time shifting. You can see that there has been very little on-peak usage (red indicator) before April 12th. Once the ESA inspection is completed, we turned on our solar panels for the first time.
The erratic “usage” indicated in the above chart after April 12th, is a direct result of excess solar energy being exported back to the grid. Since our net meter has yet to be installed, Alectra sees it as usage, and unfortunately I will have to pay for that generation, very ironic if you ask me.
Nevertheless, we gathered much data in the last couple of weeks. We tested the system for both on grid and off grid operations. We tested with washer and dryer loads. Today on a bright sunny day, I even tried our air conditioner when we are off grid. The air conditioner started without any issues and worked with just solar energy, impressive. I will try again at night when we only use the batteries.
Let us take a look at our energy generation data that we collected so far. The information here is a surprise to us in a good way. The best way to show this is to provide the data for our best day performance to date.
Our best performance day (April, 20th), 103.63 kWh generated
On April 20th we had a beautiful sunny day. We generated 103.63 kWh of electricity, since the house could not use it all, we fed most of it back to the grid. This is an excellent run and really show what the panels are capable of. For comparison, our average daily use is between 30 to 40 kWh. This means our solar generation ability on a sunny day can easily cover 2.5 to 3 days. For those Tesla drivers out there, we can generate enough power to fill your “tank”.
A rainy and cloudy morning and the sun came out at around 3pm. Total generation: 32.53 kWh (not whole day)
Yesterday was a rainy and cloudy morning, and the power generation on average kept up with house load usage. We woke up with the batteries at about 50% charged and the system managed to gain around 10% of battery charge at 3pm. After 3pm, the sun started to come out and the batteries charged rapidly. It easily reached 87% state of charge, and I had to shut the solar generation down at around 5pm, otherwise the energy would have no place to go, which leads to another major dilemma for off grid operation.
During on grid operation, the grid can regulate and absorb the excess energy generated by our solar panels. This is a huge convenience, which until we have the net meter, we really cannot take advantage of.
During off grid operation, we must use all the energy generated. Our supply must match demand and vice versa. This is where the batteries come in. They help to buffer or store the excess, and supplement any shortages. However, when the batteries are full and our usage cannot keep up with the generation, then the best option is to shutdown the solar, and shift our energy consumption to the batteries. Using the batteries will create more “empty” capacity, which we can later use to store more sun energy. I assumed, incorrectly, that this power regulation will be handled by the Schneider inverters. This is not the case, at least not fully. I am not going to go into details of Frequency Shift Power Control and other inverter deficiencies here, but suffice it to say that they are really not that smart. We will have to investigate on a more flexible power regulation mechanism for off grid operations in the future.
In the meantime, I have developed something myself that will monitor battery usage and solar power generation, so that I can determine when to turn on the solar and when to turn it off. Note that this is only for off grid operations. Once we have the net-meter, we can go back to on grid operations, and the convenience of the grid can act as the main regulator of power.
However, this is excellent experience as it teaches us some of the off grid challenges. There is no substitute for living through the experiences.
We hope the net-meter will arrive soon. Until then, we will challenge ourselves to see how many days we can stay off grid! You can already see our progress on the 23rd and the 24th of this month from the above Alectra utilization chart.
On March 31st, I saw the following picture from my garage security camera:
The Panels Have Arrived!
It took several days to install the 56 335W panels from Canadian Solar. We just finished the installation yesterday and we are now awaiting for ESA inspection and commissioning the system.
The weather was borderline cooperative, being wet and fairly high wind situations (gusting near 50 to 100 km/h at times). However the installers from New Dawn Energy Solutions soldiered on and completed the installation yesterday.
Instead of me blabbing about how the install went, here is a short video on the near daily progress.
Near Daily Progress of Installation
The system is now ready to generate power as soon as ESA inspection is completed and our power meter is changed for net metering. Hopefully this will happen in the next week or so.
In an earlier posting, I outlined how we initiated our solar panel project. Although the current weather condition prevents us from installing the solar panels at this point, we can install all of our required inverters and backup batteries.
On February the 22nd, we connected our Schneider Hybrid inverters to the grid, and on the 23rd, we connected the Pylontech LiFePO4 (LFP) batteries.
We configured the inverters so that the batteries will be discharged during the peak hours and charged during off-peak hours, effectively performing consumption time-shifting so that we can take advantage of the lower rates:
From Alectra Utilities
As you can see the savings are quite significant, more than 50%.
On February the 24th, was our first full day of usage when we tested our time-shifting configuration, and we found that it worked quite well. The battery capacity was enough to cover all of our on-peak hours usage save for the last remaining on-peak hour period.
Notice that we have more green in the off-peak hours because we are storing that capacity in the form of battery storage. I will play around with the configuration some more to see if I can shift the uncovered, on-peak hour to the mid-peak period, so that I have enough battery capacity left to cover all the on-peak periods.
I want to give a big shout out to New Dawn Energy Solutions. They have been very professional and really know their stuff. Any one thinking of installing a solar and/or a battery backup solution within the Greater Toronto Area, should seriously consider them. I highly recommend them and hope to do more business with them in the future.
Stay tune, and I will continue my progress here on the blog.
This spring, I installed solar panels on our green house. This project gave me the experience and knowledge of what I wanted for our house. In August of this year, we finally took the plunge and initiated our solar project for our house.
After much research, I settled with the following three vendors:
They all had a web presence and I initiated contact either by phone or with their online registration. For all three, I provided my postal code, my utility bill or usage, and they were able to prepare a quote for me to review. My initial request was for a grid-tie hybrid solution consisting of: Solar panels, and batteries. Specifically, I wanted to perform a full backup of my house electrical demands in the case of power outages. I wanted to avoid a typical solar only, net-metering, grid-tie solution. I also did not want a partial backup solution where certain high inductive loads such as air conditioners and dryers will not be available.
All three vendors came back with a simple solar net metering solution, the one that I specifically said I did not want. New Dawn Energy Solutions was the only vendor that gave me multiple options, one of which was a partial backup solution, which did not meet my full house backup requirement. With this initial misunderstanding, I thought it would be best that I spent sometime detailing exactly what my requirements are. I proceeded to create a slide deck with this purpose.
Long story short, getting a common understanding of my requirements was still a challenge for the vendors with the exception of New Dawn Energy Solutions. I was able to directly contact the engineer who prepared and designed the solution. This was during the weekend, and we were able to quickly clarify what I wanted and what New Dawn Energy Solutions can provide.
I decided to select New Dawn Energy Solutions and proceeded with a contract with them. While we await for permits, New Dawn Energy Solutions also helped me to start my energy audit for the Canada Greener Home Grant Program. Under this program, we can potentially get up to $5000 CAD back. The first of two audits was already performed by EnerTest. The auditor was super friendly, detailed, informative, and efficient. I would recommend EnerTest if you are going after the same program.
The current solution look something like this, but it is subject to change after an on site engineering assessment.
Our Solar Setup
As of this writing, the first energy audit is now completed. Now we will await for the engineering assessment and the required permits.
I am excited to generate clean energy and will no longer be guilty of enjoying the full capabilities of my air conditioner during the summer heat.
This is an update to my Sunroom Project that I detailed in a previous post.
After the installation of the solar panels, there was a question of whether the solar panels had enough juice to keep the batteries charge for cloudy days or night time operations. After a few days of operation, the observation is a definitive “no”.
The overall load of water pumps, fans, and temperature sensors amounted to be about 80W. The two solar panels (100W each, equaling 200W) during sunny days will only yield enough to cover this load. The less than optimal positioning on the sunroom’s roof will deprive the solar panels in operating in their optimal efficiency. Even on a really sunny day the panels may have a little surplus to give back to the battery, but nothing close to offer a continuous charge to the battery. Most of the time, the solar power is just enough to power the load and leave the battery as is. Left unattended, the batteries will slowly drain to nothing, as it is being discharged during cloudy days and at night times.
Automatic Transfer Switch from Amazon
So much for going entirely off grid! Since it is a sunroom, the roof based real estate is a bit precious, and two panels is as much as we wanted to take away from the sunshine that feed the plants. Not all bad news, we still have the opportunity to time shift our power needs from the grid, from peak time to non-peak time.
For the past few days, I had to go out to the sunroom during the evenings and switch the battery from solar power and back to the grid via the 480W DC Power Supply, so that it will charge itself back during the night. This is of course super inconvenient. What I needed is an Automatic Transfer Switch (ATS). Something like the one shown on the left offered by Amazon.
The price was pretty exorbitant, over $150.00, much more than what I wanted to spend. When there is a need, there is an opportunity to invent. I thought this is such a good opportunity to create my own ATS.
My ATS will be a simple 12V relay powered by the battery itself, and controlled by a WiFi capable microcontroller like the ESP32S that is perfect for the job. With a bit of searching on Amazon, I found this gem, a simple 12V relay that is only around $16.
URBEST 8 Pin JQX-12F 2Z DC 12V 30A DPDT
At most, the relay only needed to handle 10A, so the 30A rating is a total overkill, but good enough for my purpose.
I already have an ESP32S that I purchased earlier from AliExpress or Ebay. This is a WiFi enabled micro controller that can be programmed with the popular Arduino IDE. They were less than $5 a piece when I got them, and was literally sitting on my shelf awaiting for a project such as this. The master plan is as follows:
click to enlarge
The EPS32S will remotely control the relay, which physically makes contact between the battery with either of the solar controller or the power supply. The when is determined by a remote server on the same home network. The ESP32S will periodically post the battery voltage status and the current state of the relay to the server.
Using this approach, I can place the majority of the smarts on the server instead of the micro controller. I can also change the logic without having to reprogram the ESP32S.
The ESP32S comes with many GPIO pins. We will make use of three of the GPIO pins, one to detect battery voltage via a voltage divider. The other two will send a pulse to a simple latch that will drive the switch position of the relay. The latch will use a popular NE555 chip in bistable mode. Here is a simple schematic that I put together.
click to enlarge
I prototyped the above circuit on a breadboard and using a desktop power supply to simulate the battery.
Everything worked as expected, and I proceeded to solder everything up on a PCB.
Below is the Arduino sketch that I wrote for the ESP32S to report the battery voltage and the relay switch state to my server.
#include <WiFi.h>
#include <HTTPClient.h>
/* Server and WiFi configurations are fake */
#define SERVER_IP "192.168.1.5"
#ifndef STASSID
#define STASSID "##############-iot"
#define STAPSK "##################"
#endif
#define uS_TO_S_FACTOR 1000000
#define BATT_VOLTAGE_GPIO 36
#define GRID_PULSE_GPIO 25
#define SOLAR_PULSE_GPIO 26
float volt = -1.0;
RTC_DATA_ATTR int currentState = -1;
void setup() {
pinMode(BATT_VOLTAGE_GPIO, INPUT);
pinMode(GRID_PULSE_GPIO, OUTPUT);
pinMode(SOLAR_PULSE_GPIO, OUTPUT);
digitalWrite(GRID_PULSE_GPIO, LOW);
digitalWrite(SOLAR_PULSE_GPIO, LOW);
Serial.begin(115200);
Serial.printf("Connecting to %s..\n", STASSID);
WiFi.begin(STASSID, STAPSK);
while (WiFi.status() != WL_CONNECTED) {
delay(250);
Serial.print(".");
}
Serial.print("\nConnected with IP: ");
Serial.println(WiFi.localIP());
}
void pulse(int pin) {
digitalWrite(pin, HIGH);
delay(200);
digitalWrite(pin, LOW);
}
// the loop function runs over and over again forever
void loop() {
WiFiClient client;
HTTPClient http;
digitalWrite(LED_BUILTIN, HIGH);
float v = 0;
for (int i = 0; i < 200; i++) {
v += analogRead(BATT_VOLTAGE_GPIO);
delay(2);
}
volt = v / 200.0;
Serial.print("Voltage Read: ");
Serial.println(volt);
http.begin(client, "http://" SERVER_IP "/autoTransferSwitch.php"); //HTTP
http.addHeader("Content-Type", "application/x-www-form-urlencoded");
// start connection and send HTTP header and body
String postStr = "id=sunroom";
postStr += "&volt=" + String(volt);
postStr += "&state=" + String(currentState);
int httpResponseCode = http.POST(postStr);
digitalWrite(LED_BUILTIN, LOW);
Serial.printf("Response code: %d\nResult: ", httpResponseCode);
String instructions = http.getString();
Serial.println(instructions);
String result = "nothing";
long sleepTime = 5L;
char buffer[100];
strncpy(buffer, instructions.c_str(), 100);
const char d[2] = ",";
int field = 0;
char* token = strtok(buffer, d);
while ( token != NULL ) {
if (field == 0) {
result = String(token);
}
if (field == 1) {
sleepTime = atol(token);
}
token = strtok(NULL, d);
field++;
}
if (result.equals("solar")) {
pulse(SOLAR_PULSE_GPIO);
currentState = 1;
} else if (result.equals("grid")) {
pulse(GRID_PULSE_GPIO);
currentState = 0;
} else {
digitalWrite(GRID_PULSE_GPIO, LOW);
digitalWrite(SOLAR_PULSE_GPIO, LOW);
}
http.end();
Serial.print("Sleeping for seconds: ");
Serial.println(sleepTime);
esp_sleep_enable_timer_wakeup(uS_TO_S_FACTOR * sleepTime);
esp_deep_sleep_start();
}
One nice thing about the ESP32S is its ability to go into a deep sleep where it can keep its state with almost zero power. This way, the micro controller doesn’t act as a power sink for the entire system. I took advantage of this feature, so that the server can also tell the ESP32S how long it should sleep.
On the server side, I have a simple PHP script that will take into account time of day, and the current battery charge.
<?php
date_default_timezone_set('America/Toronto');
// I've changed the location to protect my own privacy
$lat = 42.9293;
$log = -102.9478;
$zenith = 90;
$nextWait = 900;
// The voltage levels are ADC readings from ESP32 (divided by 10) and not actual volts
// voltage level when battery is fully charged and can either be used or be charged with solar
$solarChargeLevel = 280;
// voltage level when battery is okay to be used with or without solar (come off of grid)
$okChargeLevel = 260;
// voltage level when battery must be charged (get on grid)
$mustChargeLevel = 252;
$now = time();
$sr = date_sunrise($now, SUNFUNCS_RET_TIMESTAMP, $lat, $log, $zenith);
$ss = date_sunset($now, SUNFUNCS_RET_TIMESTAMP, $lat, $log, $zenith);
$srStr = date("D M d Y - h:i:s", $sr);
$ssStr = date("D M d Y - h:i:s", $ss);
$logFile = "/home/kang/log/autoTransferSwitch.log";
$dateStr = date("Y-m-d H:i:s");
header("Content-Type: text/plain");
$id = isset($_POST["id"]) ? $_POST["id"] : null;
$batVolt = isset($_POST["volt"]) ? $_POST["volt"] : null;
// -1 = initial, 0 = grid state, 1 = solar state
$currentState = isset($_POST["state"]) ? intval($_POST["state"]) : -1;
file_put_contents($logFile, "$dateStr, " .
"device reported: battery voltage: $batVolt and current state: $currentState\n",
FILE_APPEND);
if (!is_null($id)) {
if ($id === "sunroom") {
$action = "nothing";
$b = intval($batVolt) / 10.0;
// During day is defined by one hour after sunrise and one hour after sunset
$duringDay = (($sr + 3600) <= $now && $now <= ($ss - 3600));
$duringNight = (!$duringDay);
if ($currentState == -1) {
if ($b <= $mustChargeLevel) {
$action = "grid";
$currentState = 0;
} else {
$action = "solar";
$currentState = 1;
}
} else if ($currentState == 0) {
// We are charging from the grid
if ($duringDay && $b >= $okChargeLevel) {
// During the day we want to use solar or the battery as much as possible;
// This is a trickle charge so that we can take advantage of the sun.
$action = "solar";
$currentState = 1;
} else {
// Otherwise charge until battery is full
if ($b >= $solarChargeLevel) {
$action = "solar";
$currentState = 1;
}
}
if ($b >= 0.985 * $solarChargeLevel) {
// We are getting closer to fully charge so
// reduce communication interval from 15 min to 5 min
$nextWait = 300;
}
} else if ($currentState == 1) {
// We are either using the battery or the solar panels
if ($b <= $mustChargeLevel || $now > $ss + 3600) {
// Charge the batteries if we must or one hour past sunset
$action = "grid";
$currentState = 0;
}
if ($b <= 1.025 * $mustChargeLevel) {
// We are getting closer to require charging so reduce
// communication interval from 15 min to 5 min
$nextWait = 300;
}
}
// for testing purpose
// $nextWait = 15;
echo ($action . "," . $nextWait);
file_put_contents($logFile, "$dateStr, $batVolt, $action, " .
"sun: [$srStr - $ssStr], new state: $currentState, wait: $nextWait\n",
FILE_APPEND);
}
}
The above state transition logic is pretty simple to follow so I am not going to explain it in depth here. There are a couple of features that I like to expand on.
By default, the sleep time is 15 minutes, but the server will shortened it to a shorter interval of 5 minutes when the battery is near empty or full. This sample frequency should be enough for the server to make the appropriate switching decision. Once a switch in the relay has occurred, the sleep time can be reverted back to 15 minutes. For debugging purposes, I can also change the server script to a very fast sample rate of every 15 seconds.
The other feature is the account of day and night time. This first version of the algorithm will attempt to use solar and/or battery during the day, and only charge from the grid when it is absolutely necessary. If we do charge from the grid during the day, we don’t need to fill it up, but only charge it to a level that can be used again. We will then attempt to top up the battery about 1 hour after sunset.
My ATS is now installed and operating for an entire day, so far so good and I don’t have to go into the sunroom any more to perform a manual switch. The algorithm can be further enhanced by getting additional readings from the solar controller, but I didn’t want to go through the trouble. I think what I have so far should be sophisticated enough. We’ll see.
2021-06-18 Update: After several days of operation, I noticed that the ATS, more specifically the ESP32 micro-controller hangs or fails to wake from deep sleep after a few hours of operation. Upon further investigation, it may be a combination of unstable supply voltage (from the battery), memory leaks of the standard WiFi libraries or the usage of String types. I am not sure. I had to re-write my ESP32 Arduino sketch to include a watch dog reset as well as perform a timed, software triggered hardware reset of the controller itself every 30 minutes or so. I also eliminated the deep sleep functionality and simply resorting to delays and resets. It has been running for about a week without any hiccups.
YouTube viewing has been one of our favourite pass times during the lock down nature of the Covid-19 pandemic. I personally have been watching quite a few channels on how to use LiPO4 cells to build rechargeable battery banks for solar applications, primarily for off grid purposes.
We have a sunroom in our back yard that we used during the summer to grow some vegetables. It has some electrical needs such as water pumps, a temperature sensor, and a fan. Currently there is an electrical socket, fed from the house, that we plug these devices into. We thought it would be a good project to try to get our sunroom off grid. This would be a good learning project.
The first task is to build a 12V LiFePO4 prismatic cells battery bank. I purchased 4 3.2V 100Ah battery cells from AliExpress. The cells came with bus bars so I did not have to purchase those. However, I did have to buy a battery management system (BMS) to balance and manage the charging and discharging of the battery cells. It was very tempting to buy a BMS from AliExpress, but I decided to be cautious and purchased one from a US vendor with the accompanying and preferred quality control. The company Overkill provides a 12V BMS specifically for four LiFePO4 battery cells in series.
It took a very long time for the batteries to arrive from China. I suppose the pandemic could be one of the many reasons for the delay. Once they arrived, I connected in parallel and proceeded to perform a top balance procedure with my voltage limiting desktop power supply. This step is required because each cell will have a different voltage potential from each other. We want all the cells to have the same voltage potential to maximize the capacity that we will get from the aggregated 12V battery bank.
Cells in parallel being topped balanced at 3.65V until zero current
To top balance all the cells, first I hook up the cells in parallel and charge them at a constant voltage of 3.65V. The charge will continue until my desktop power supply shows zero amp going into the battery. This process took a very long time, almost 2 days.
Once the cells are balanced, I reconfigured the cells in series and proceeded to hookup the BMS and the pure sine wave 600W inverter I purchased from Amazon. I had to buy 4 AWG wire, once again from Amazon, because the 10 AWG wire that I purchased earlier was not going to be enough if I want to discharge the battery at 600W which is going to result in more than 50A of current at 12V. I used the remaining 10 AWG wire for solar controller and panel hookups. I also got some XT90 connectors so that I can easily plug/unplug the solar charge controller, solar panels, and potentially plugin charger. I will talk about the solar side some more later on.
All wired up. The yellow XT90 connector is to either a solar charge controller or an external DC charger
So now that we have the guts of our 12V LiFePO4 battery pack, we need to find a suitable home for this thing. My wife had an extra plastic filing box hanging around which is perfect for this.
A filing box is perfect to fit everything
Custom grommets and added a PC fan
I needed to drill some holes to fit a 12V 120mm PC fan for ventilation, and a couple of 2″ grommets so that we can pass plugs and connectors through the box. The fan will be powered by the inverter.
At this point we have ourselves a 1200Wh portable super battery pack that can power up to 600W of electronics, which will be great for road trips. If you plug a 20W iPhone fast charger and charge your phone, it can continuously charge for 60 hours (2.5 days). That is a lot of phones. If your MacBook Air ran out of juice on the road, then this battery pack can power a 45W charger for your MacBook Air for more than a day, and also charge your computer fully. Quite a handy thing to have for emergencies.
Doubles as a 1200Wh portable battery bank
For the solar panels, I purchased two Xinpuguang 100 W flexible solar panels from Aliexpress. They were about $1 / Watt, a pretty good deal. I hook the two panels together in series and got a Victron BlueSolar MPPT 75/10 solar charger to manage the charging of the batteries. The charge controller can accept a maximum of 75V and outputs a maximum of 10A.
The charge controller will automatically adjust the amperage and voltage to the battery bank as required ensuring optimal charging scenario. During a sunny day, it will run the sunroom load from the panels and any remaining current will goto charge the battery. At night, the battery will run the sunroom.
Today, we installed the entire setup. The battery is placed inside the green house to give it some precipitation protection.
The panels are latched to the roof of the green house, one on each side.
The BMS unit has a bluetooth connection and an iOS App. I can use my iPhone when in bluetooth range of the battery to see if the battery is being charged or discharged.
I took the following screen shot of the app today at around 5pm EDT. You can see that there is no current going into the battery and no current going out of the battery. This means the sun is powerful enough to run all the pumps and other electrical appliances in the sunroom. Pretty cool!
It is still too early to tell yet whether there is enough sun power to charge the battery and run the electrical devices in the sunroom in a sustainable manner. My current suspicion is that the two panels are just enough even on a full, bright, sunny day and at peak hours, to power devices and also provide surplus current to charge the batteries.
Here is my overall connectivity diagram:
We will let the system run for about a week to see if this is sustainable during the summer months or not. If not, then I will have to create an automatic transfer switch so that we can intermittently recharge the batteries during the evening with an optional 480W DC charger, which I also got from Aliexpress. This charger can operate between 0-24V and 0-20A. To charge the battery bank, I have set it to a constant voltage of 14.0V and allow the output current to flow unrestricted. This should charge the battery fully in a little over 4 hours from scratch.
Overall, I learned a lot from this project and what a great way to spend the pandemic indoors. This could be a precursor to a DIY Tesla Powerwall Project. We’ll see.
